Power supplies for charging batteries are well-known, and numerous types have been constructed, and are commercially available. Such battery chargers are conventionally large, heavy and bulky devices, which provide a constant voltage, which is either manually applied to and removed from terminals of a storage battery, or timed with a timer which de-energizes the battery charger after a predetermined length of time. For charging a battery as quickly as possible, some such power supplies have been provided with a fragile temperature measuring means to be inserted into the electrolyte of a cell to measure its temperature, and disable the output of the battery charger to prevent temperature of the electrolyte from exceeding a predetermined value. Numerous other features have been incorporated in battery chargers, such as a variety of charging modes, including boost charges, trickle charges, charging with a sawtooth waveform, so-called "burp" circuits in which a short pulse of high voltage is applied in a direction opposite the direction of charging current to dislodge evolved gas bubbles, timer circuits for applying charging current in a predetermined pattern of voltage steps, and the like.
Battery chargers have been constructed using ferroresonant transformers, adjustable air gap transformers, and leakage reactance transformers with an interruption or air gap in the magnetic circuit.
These prior battery chargers, in addition to being large and bulky, were not well-suited for charging a storage battery which was only partially discharged.
The disclosed battery charger overcomes these and other deficiencies of the prior art.